The exemplary embodiment relates to a method for straightening hair by application of heat and to a composition which can be activated by heat comprising a heterocyclic compound containing two heteroatoms selected from nitrogen and oxygen in a 5 or 6-membered ring, such as a cyclic alkylene carbonate.
Various methods are available for semi-permanent and permanent straightening of hair which can maintain the hair in a modified state for several washes. Many of the permanent treatment methods make use of harsh chemicals which can be hazardous to those performing and receiving the treatment or which give off unpleasant odors. Some of these methods are based on cleavage of the cysteine disulfide covalent bonds that are present in keratin. In one method, the disulfide bonds are first broken with a reducing agent. Then a fixative, such as hydrogen peroxide, is applied while the hair is under tension to reconstitute the disulfide bonds in a different arrangement. The peroxide can cause damage to the hair and scalp. Other methods use a hydroxide base which replaces the disulfide bonds (—CH2—S—S—CH2—) with lanthionine bonds (—CH2—S—CH2—) in a two stage process using a hydroxide ion in the first step and a thiol group in the second. The hydroxide is used at fairly high concentrations and can cause scalp burning, and irritation or damage of the eyes and nose. Thiols leave the hair with an unpleasant odor and can lead to degradation of the hair fibers.
Semi-permanent methods use a cross-linking agent to form bonds while the hair is heated. Formaldehyde, for example, is used in many commercial straightening products, either as an ingredient of the composition or as a reaction product that is formed on heating of the hair. However, it can cause allergic reactions to the skin, eyes and lungs, can cause severe damage to the eyes, and poses other health risks. The use of formaldehyde in hair straightening compositions has been discouraged or banned in some countries but it remains in widespread use, due to its effectiveness. Relaxing compositions including a denaturing agent such as urea have also been proposed. However, while urea is less caustic than a hydroxide-based composition, it can decompose to ammonia and poisonous isocyanic acid at the high temperatures used for thermal hair straightening.